Method of pretreating metallic hydrides



May 7, 1968 J. E. LINDBERG, JR 3,332,048

METHOD OF PRETREATING METALLIC HYDRIDES Filed March 18, 1965 "M l A9INVENTOR.

J.E. LINDBERG,JR.

ATTORNEY United States Patent 0 3,382,048 METHOD OF PRETREATING METALLICHYDRiDES John E. Lindberg, Jr., 1211 Upper Happy Valley Road, Lafayette,Calif. 94549 Continuation-impart of application Ser. No. 176,095,

Feb. 27, 1962, which is .a continuation-in-part of application Ser. No.65,891, Oct. 31, 1960, which is a division of application Ser. No.815,406, May 25, 1959, now Patent No. 3,122,728. This application Mar.18, 1965, Ser. No. 440,857

7 Claims. (Cl. 23-316) ABSTRACT OF THE DISCLOSURE A method ofpretreating a metallic hydride, usually a powder, of the type thatcontains some oxide impurities and that emits hydrogen when heated hotenough and takes it back in when cooled, the purpose of the pretreatmentbeing to assure consistent ingassing and outgassing in a closed system.The hydride is heated in said system, preferably electrically, to atemperature well above its threshold temperature, so that it outgasseshydrogen and becomes stabilized with respect to the oxides; the hydrideis then cooled to well below the threshold temperature to reingas someofthe hydrogen; then the hydrogen that did not reingas is withdrawn fromsaid system until a desired pressure level is reached; then the closedsystem is sealed. The system may be substantially evacuated while andafter withdrawing the hydrogen that did not reingas and filled beforesealing with an inert atmosphere, comprising helium, neon, argon,krypton or xenon gas.

This application is a continuation-in-part of application Ser. No.176,095, filed Feb. 27, 1962, which was a continuation-in-part ofapplication Ser. No. 65,891, filed Oct. 31, 1960, both now abandoned,which was a division of application Ser. No. 815,406, filed May 25,1959, now Patent No. 3,122,728.

This invention relates to a method of pretreating metallic hydrides, toassure consistent ingassing and outgassing in a closed system.

When most metal hydrides (whether true compounds or solutions ofhydrogen in metal) are procured, it will generally be found that theyare, so far as use in temperature detectors is concerned, over-chargedwith hydrogen. As a result, if they are heated in a closed system andthen cooled, they will not reingas all the hydrogen which they emittedwhen heated. Moreover, the reingassing and outgassing thenceforward tendto be erratic and undependable, and the pressure in the closed systemdoes not therefore truly correspond to the temperature to which thatsystem is exposed.

The art recognizes alpha, beta, gamma and so on states of some metallichydrides, containing different amounts of hyrogen induced under varyingconditions. When such a hydride is outgassed into a relativelylowpressure atmosphere, such as an 18.7 p.s.i.a. argon atmosphere in asensor chamber described in the parent application, I have found that itwill not fully reingas when it cools to its original temperature, forthe original conditions needed to cause such ingassing is not present.On repeated outgassing and ingassing, the amount ingassed tends tobecome progressively less, or to be erratic because of impuritiescontained in the original hydride which tend to interfere with thenormal phenomena of ingassing and outgassing of hydrogen. I have foundthat oxides, a probable impurity to which little attention has been paidheretofore in this regard, tend to be particularly troublesome. I havefound that the prior art does not yield constant and uniform results infire detectors probably due to these oxides.

This problem is solved in the present invention by pretreating thecommercial grade hydride both to achieve stabilization of the oxides andto convert the hydride into a stable compound or solution assuringrepetitive and standardized results. The invention applies to allmetallic hydrides of the type that emit hydrogen when heated above athreshold temperature, including hydrides of the alkali metals (lithium,sodium, potassium, etc.), the alkaline earth metals (calcium, barium,stontium, etc.), scandium, titanium, vanadium, palladium, ytter bium,zirconium, niobium, hafnium, tantalum, the rare earth metals (atomicnumbers 57-71), and the actinide metals (atomic numbers 89 and on).

Another problem has been that of minimizing the transfer of the metalcomponent of the hydride from one part of the tube to another duepossibly to deposition at times when the hydride is outgassed. This hasbeen a more severe problem than might be thought because some of thistransfer has resulted in deposition of the metal onto the walls of thetubing of a fire detector containing the hydride. Moreover, thistransferred metal has tended to diffuse itself within or upon the wallswhen they are metal, and the resulting alloy has tended to melt at amuch lower temperature than the encasing metal of the tube. The resulthas sometimes been that holes would develop in the tube.

This vapor deposition problem I have found can be solved by including inthe tube a gas which is inert with respect to the tube walls and to allthe components in the tube. Helium and argon and other noble gases aresatisfactory for this purpose. They appear to suppress this transfer,though I am not certain as to the mechanism involved or whether anycurrent theory accurately explains how it is done.

Another problem has occurred when twohydrides have been used, one to usewith a testing apparatus, the other as the actual sensor in a firedetector. Before this invention, there was a tendency for the hydrogento transfer from one hydride to the other, with resultant changes in thecharacteristics and action of both of them.

The invention has solved this last-mentioned problem by using differenthydrides with different threshold temperatures, as will be explained.

Other obects and advantages of the invention will appear from thefollowing description.

The drawing is a somewhat schematic view showing on an enlarged scale afire detection device in which the invention is practiced and anelectrical current therefor. The main sensor tube has been broken in themiddle to conserve space.

The drawing shows a fire-detection sensor 1, comprising a tube 2,preferably of an austenitic stainless steel, closed hermetically at oneend by a cap 3 and containing a metallic hydride 4 such as titaniumhydride, which may be in chunk form or in another form. The sensor 1 hasan open end 5 that opens into a responder 6 at a chamher 7. Theresponder 6 has a diaphragm 8 clamped hermetically into a housing madeup of two plates 9 and 10. The diaphragm 8 preferably has a dome-shapedblister 11, which is the active presure-sensitive element thereof, andon the opposite side of the diaphragm 3 is a contact member or electrode12, located in a ceramic tube 13, which is also hermetically sealedafter its interior 14 is set at a desired pressure. A wire 15 leads outfrom the tube 13 to a warning lamp 16, when a lead 17 goes to connect toa battery 18 or other source of electric power. The other side of thebattery 18 may be grounded at 19, and the housing plate 10 may begrounded at 28 (or there may be a return wire), to complete the circuit.Normally the circuit is open, but when the gas pressure in the chamber 7is sufficient to move the blister or dome 11 into contact with theelectrode 12, the circuit is completed and the lamp 16 is lighted.

A test unit 21 may comprise a ceramic tube 22 containing a differentpowdered hydride 23 held in by a porous plug 24. The tube 22 isconnected by a hole 25 through the diaphragm 8, with the chamber 7. Anelectrical filament 26 goes through the tube 22 to enable artificallyheating the hydride 23. The tube 22 is hermetically closed by a cap 27and is hermetically sealed to the plate 9. A wire 28 leads from thefilament 26 via an insulator 29 to a normally open switch 36 and thenceto the battery 18. Closure of the switch heats the filament 26.

An example of practicing this invention is in making a device like onein the parent application, wherein the housng or tube 22 contains thetest device 21 comprising the contained filament 26 and powderedmetallic hydride 23, such as that of tantalum, titanium, vanadium, orpalladium, the whole is purged, as described in the parent applicationand in its related case, Patent No. 3,153,847, and, near the end of thepurging process, a vacuum is pulled on both ends. At this time themetallic hydride 23 is reconditioned by filling the tube and any otherparts of the closed system, if any, with hydrogen at one atmospherepressure (14.7 p.s.i.a.) at room temperature. Then the filament 26 isheated well above the threshold temperature for that particular hydride23, e.g., to about 1,000 C. for titanium, by passing a current throughit. This heat not only causes the hydride 23 to emit hydrogen; it alsoapparently frees the hydride of its oxides; those which remain arebelieved to be rendered inert in the hydride, and once treated they donot give trouble and produce no significant effect. Anotherinterpretation is that this heat cracks oxide coatings, providingfissures that thereafter afiord entry to the metal. The filament 26 isthen permitted to cool to room temperature, or at least to a temperaturewell below the threshold temperature, while the hydride reingasses. Atroom temperature, the excess hydrogen that remains in the atmosphereafter reingasing is withdrawn. Preferably, the tube 22 is evacuated ofall the hydrogen gas and filled with an inert atmosphere, such as argonor other noble gas, at any desired pressure, such as 18.7 p.s.i.a. Thedesired pressure may be obtained by letting some of the hydrogen gasremain, still withdrawing the excess, but the inert argon or helium isbetter for preventing transfer of the dehydrided metal at hightemperatures or during outgasing, when it otherwise tends to migrate anddepart on the walls 26 by vapor depositions.

When the tube 22 is used on a test device 21 in combination with theheat-detecting sensor 1 containing hydride of the same group of metals,as disclosed in my co-pending application Ser. No. 271,043 filed Apr. 1,1963, now Patent No. 3,277,860 a continuation-in-part of applicationSer. No. 102,622, filed Apr. 10, 1961 and now abandoned, the hydride 23in the testing tube 22 with the electric filament 26 should be of ametal hydride that ingasses and outgasses at a lower thresholdtemperature than that in the heat detecting sensor 1, in order that thesensor hydride 4 not be affected by opt eration of the electricallyheated hydride. This can be determined by tables. For example, palladiumhydride and vanadium hydride outgas at lower threshold temperatures thanzirconium hydride, so they can be used in a test unit 21 with a sensor 1having zirconium hydride.

For getting rid of the oxides, a high temperature is needed during thepro-treatment. For example, dissolution of the oxides in titaniumhydride is best obtained by heating to about 2,000 P. under vacuumconditions. The necessary heating, in all instances, is preferably doneelectrically, as by the filament 26, because precise temperature controlis thereby obtained.

The invention is useful with hydrides (solutions or compounds) of alloysand with mixtures of alpha, beta, gamma, etc. hydrides as well as withany one state.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departmentfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

I claim:

1. A method of pretreating for use in closed system, a metallic hydrideof the type that emits hydrogen when heated and takes it up when cooled,in order to assure consistent ingassing and outgassing in a closedsystem, consisting essentially of: heating said hydride in said closedsystem to a temperature that will outgas its hydrogen into said system;cooling said hydride to a desired temperature well below the outgassingtemperature for that particular hydride in that system, to reingas asmuch of the hydrogen as will reingas under the pressure conditions thenobtaining in said system; and withdrawing from said closed area thehydrogen that did not reingas until a desired pressure level in thesystem is reached, adjusting the final pressure level in the system toatmospheric pressure at room temperature, and sealing said closedsystem.

2. A method of pretreating a metallic hydride of the type that emitshydrogen when heated above an outgassing temperature and takes it upwhen cooled therebelow to assure consistent ingassing and o-utgassing ina closed system, said hydride normally containing some oxides comprisingheating said hydride to above its outgassing temperature and to atemperature sulficient for dissolution of the oxides therein in acontainer forming part of said closed system, to o'utgas hydrogen intosaid closed system, cooling said hydride to a temperature below saidoutgassing temperature so that the hydride reingasses a stable amount ofthe hydrogen, then withdrawing from the closed system the hydrogen thatdid not reingas and then sealing said closed system, thereby leaving thehydride in a stable state in a closed system whereby it thereafteringasses and outgasses repetitively to impart to the system a pressurehaving a one-to-one correspondence with the temperature of the hydride.

3. A method of pretreating a metallic hydride of the type that containssome oxide impurities and that emits hydrogen when heated hot enough andtakes it back in when cooled, to assure consistent ingassing andoutgassing in a closed system, comprising electrically heating saidhydride in said system to a temperature well above its thresholdtemperature, thereby causing it to outgas hydrogen and to stabilize withrespect to the oxides, cooling said hydride to well below said thresholdtemperature to reingas some of the hydrogen, then withdrawing from saidsystem the hydrogen that did not reingas until a desired pressure levelis reached, and then sealing said closed system.

4. The method of claim 3 wherein said system is substantially evacuatedwhile and after withdrawing the hydrogen that did not reingas and thenis filled with inert atmosphere.

5. The method of claim 4 wherein said inert atmosphere comprises gaschosen from the group consisting of helium, neon, argon, krypton, andxenon.

6. The method of claim 5 wherein said gas is argon.

7. A method of pretreating a powdered metallic hydride of the type thatoutgasses hydrogen when heated above a certain temperature andreingasses when cooled, to assure consistent ingassing and outgassing ina closed system, comprising: heating said hydride in said closed systemwell above its threshold temperature to outgas hydrogen into saidsystem; cooling said hydride to about room temperature to reingas asmuch of the hydrogen as will reingas at room temperature under thepressure conditions then obtaining in said system; withdrawing from saiding a charge of noble gas to said system, and then sealing said system.

References Cited UNITED STATES PATENTS 2,497,911 2/ 1950 Reilly 250-2753,064,245 11/ 1962 Lindberg 340229 3,153,846 11/1964 Lindberg 340-2293,177,479 4/ 1965 Lindberg 340-229 FOREIGN PATENTS 812,945 5/ 1959 GreatBritain.

CARL D. QUARFORTH, Primary Examiner.

closed system the hydrogen that did not reingas; then add- 15 STEINERAssistant Examiner-

